In this project we will develop chemopreventative agents against cancer based on carcinogens present in tobacco smoke. Although smoking cessation is clearly the best way to avoid lung and esophageal cancer, there are still approximately 48 million smokers in the United States. Many are addicted to nicotine. For people who have failed smoking cessation programs, chemoprevention is a way to decrease risk for cancer. In previous studies, we have developed phenethyl isothiocyanate (PEITC) as a highly effective naturally occurring chemopreventative agent against lung cancer induced by the tobacco-specific lung carcinogen 4- (methylnitrosamino)-1-(3-pyridyl)-1- butanone (NNK). The mechanism by which PEITC inhibits NNK induced lung cancer is well understood and there are apparently parallels between rodents and humans. In spite of these promising results with NNK, PEITC has not been shown to inhibit lung tumorigenesis by benzo[alpha]pyrene (BaP), another important lung carcinogen in tobacco smoke. Our hypothesis is that chemoprevention of lung cancer in smokers will require agents that can inhibit DNA damage and carcinogenesis by both NNK and polycyclic aromatic hydrocarbons (PAH), typified by BaP. Benzyl isothiocyanate (BITC) does inhibit lung tumorigenesis by BaP. Therefore, we will investigate the mechanisms of these contrasting effects as well as extending our studies on mechanisms by which isothiocyanates and their conjugates inhibit tumorigenicity. In Specific Aim 1, we will carry out mechanistic studies designed to elucidate the basis for the contrasting effects on BITC and PEITC on BaP carcinogenesis in mice. These studies will be extended to determine whether similar mechanisms apply to the N-acetylcysteine conjugates of BITC and PEITC, in collaboration with Project 1. In Specific Aim 2, we will investigate the effects of isothiocyanates on lung tumor induction by 5-methylchyrsene and dibenz[alpha, 5]anthracene, two potent PAH carcinogens in tobacco smoke. In Specific Aim 3, we will investigate the mechanism by which a mixture of BITC and PEITC inhibits mouse lung tumorigenesis by a mixture of NNK and BaP. In Specific Aim 4, we will collaborate with Project 1 to determine the effects of watercress and/or garden cress consumption, as source of PEITC and BITC, on NNK and BaP metabolism in smokers. In Specific Aim 5, we will collaborate with Project 2 to determine the effects of PEITC and 3-phenylpropyl isothiocyanate (PPITC) on the metabolic activation of N'-nitrosonornicotine (NNN) in rats and smokers. The results of our work will provide critical new data relevant to chemoprevention if cancer in smokers.